A cardiac arrhythmia is a condition in which the heart's normal rhythm is disrupted. There are many types of cardiac arrhythmias, including supraventricular arrhythmias that begin above the ventricles (such as premature atrial contractions (PACs), atrial flutter, accessory pathway tachycardias, atrial fibrillation, and Atrioventricular nodal reentrant tachycardia (AVNRT)), ventricular arrhythmias that begin in the lower chambers of the heart (such as premature ventricular contractions (PVCs), ventricular tachycardia (VT), ventricular fibrillation, and long QT syndrome), and bradyarrhythmias that involve slow heart rhythms and may arise from disease in the heart's conduction system. Further, cardiac arrhythmias may be classified as reentrant or non-reentrant arrhythmias. In reentrant arrhythmias, the propagating wave of bioelectricity that normally spreads systematically throughout the four chambers of the heart instead circulates along a myocardial pathway and around an obstacle (reentry point) or circulates freely in the tissue as a scroll wave or spiral (referred to herein as “rotors”). In non-reentrant arrhythmias, propagation of the normal bioelectricity wave may be blocked or initiated at abnormal (ectopic) locations.
Certain types of cardiac arrhythmias, including ventricular tachycardia and atrial fibrillation, may be treated by ablation (for example, radiofrequency (RF) ablation, cryoablation, ultrasound ablation, laser ablation, and the like), either endocardially or epicardially. However, a physician must first locate the point of reentry, ectopic focus, or regions of abnormal conduction to effectively treat the arrhythmia. Unfortunately, locating the best site for ablation has proven to be very difficult, even for the most skilled physicians.
Cardiac electrical mapping (mapping the electrical activity of the heart that is associated with depolarization and/or repolarization of the myocardial tissues) is frequently used to locate an optimal site for ablation, for instance, a reentry point, ectopic focus, or a site of abnormal myocardium. However, the source of an arrhythmia may be difficult to determine based upon the sensed electrogram morphology. In addition to signals emanating from the local myocardium, the electrogram morphology may include fractionation due to poor electrode contact, electrode design, or complex electrical activity in the vicinity of the electrodes. The signals may also include “far-field” content from distant tissues (such as detection of ventricular activity on atrial electrodes) or the signal may be attenuated due to disease, ischemia, or tissue necrosis. Further, ablation of one or more identified sites may also be problematic.
To date, such ablations require either substantial trial and error (for example, ablation of all sources of complex fractionated electrograms) or the use of separate mapping and ablation devices (complex mapping systems utilizing multielectrode arrays or baskets may be used to identify an ablation site, but cannot also be used to ablate the tissue). The long term success of treating arrhythmias often depends on the determination of the exact tissue or trigger in the heart causing the arrhythmia so that the malfunctioning tissue can be ablated and the normal rhythm of the heart restored. Ablation of arrhythmias, like atrial fibrillation, whether paroxysmal or chronic, typically involves the simultaneous mapping of a region of cardiac tissue with a multi-electrode catheter in order to identify and ablate tissue sources or drivers of arrhythmias.
Mapping often includes analyzing a displayed electrogram signal in order to identify arrhythmic sites and possible ablation targets. However, in complex electrograms, as in those in patients with atrial fibrillation, the electrogram signals may include several deflections making an accurate real-time determination of target tissue regions cumbersome and ambiguous.